Influence of pore characteristics of sand strata on filter-cake formation under slurry shield

The characteristics of filter cake formation on the excavation face of permeable sand strata are the critical factors for the growth and decrease law of the soil and water pressure in the strata as well as the stability of excavation face. Then the requirement of these analyses is to establish the quantitative relationship between the pore characteristics and filter cake forming characteristics. The quantitative indexes of pore characteristics and filter cake forming characteristics are raised by carrying out the slurry filtration tests in the strata with different pore characteristics. Based on the quantitative relationship between the both characteristics, the filter cake formation laws influenced by the pore characteristics are studied. The results show that the two-parameters model for the filtration curve can describe the variation characteristics of seepage discharge. Th model parameters own clear physical significances to quantify filter cake forming characteristics such as curvature characteristics of seepage discharge, formation time and forming stages of filter cake. Based on the relationship of power function between parameters a, b and the pore volume v, the quantitative relationship of pore characteristics and the filter cake forming characteristics is established. The research results can determine the reasonable slurry proportion and construction parameters and may provide experimental and theoretical support for guaranteeing the stability of the excavation face for slurry shield tunneling projects excavated in highly permeable sand soils.